A recent study delves into the science, but doctors say there’s more to it.

Running extreme distances may strain more than just muscles and joints. New research suggests ultramarathons can alter red blood cells in ways that make them less flexible and more prone to breakdown, ...

Ultramarathons might push red blood cells past their limits—accelerating their aging in the process.

Extreme endurance running damages red blood cells in ways that may affect their ability to function properly, according to a study published in the American Society of Hematology's journal Blood Red ...